The present invention relates to a display device such as a liquid crystal display device, and more particularly to a display device which includes an illuminance detection circuit.
In general, a liquid crystal display device is rarely used in a pitch-dark state with no external light. That is, the liquid crystal display device is used in a state that an external light in any form, for example, a natural light or a light of an indoor illumination lamp is radiated to a liquid crystal panel. Under such a circumstance, patent documents 1, 2 (JP-A-2003-21821, JP-A-2002-72992) describe techniques for controlling the brightness of a backlight by measuring the brightness of surrounding of the liquid crystal display panel (that is, illuminance of an external light). In patent document 1, when the surrounding of the liquid crystal display panel is bright, the brightness of the backlight is increased so as to allow a user to easily look at the liquid crystal display panel. On the other hand, when the surrounding of the liquid crystal panel is dark, the user can sufficiently look at the liquid crystal display panel even when the liquid crystal display panel is dark and hence, the brightness of the backlight is lowered to suppress the power consumption.
Further, patent document 3 (JP-A-5-164609) discloses a technique which uses a Schmidt inverter as an illuminance-frequency converting circuit for converting illuminance measured by a photosensor into frequency.